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United States Patent |
6,163,369
|
Yamada
,   et al.
|
December 19, 2000
|
Plane position detecting method and exposing method and exposure
apparatus using same
Abstract
The position or the inclination of a substrate surface is detected at a
high accuracy and a high speed, and corrected. When moving the substrate
in a direction substantially at right angles to an optical axis of a
projection optical system and feeding an area on the substrate into an
image space of the projection optical system, at least one of the position
and inclination in the optical axis direction of the substrate is
detected, to bring that area into focus with the focal plane of the
projection optical system. One of a first mode of conducting the
measurement during travel of the substrate and a second mode of performing
the measurement in a state in which that area has substantially been
positioned in the image space is selected.
Inventors:
|
Yamada; Yuichi (Utsunomiya, JP);
Kawahara; Atsushi (Utsunomiya, JP)
|
Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
205173 |
Filed:
|
December 4, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
355/55; 355/53; 355/56; 355/71; 356/399; 356/400 |
Intern'l Class: |
G03B 027/52; G01B 011/00 |
Field of Search: |
355/53,55,56,71
356/399,400
|
References Cited
U.S. Patent Documents
4962423 | Oct., 1990 | Yamada et al. | 358/101.
|
5323016 | Jun., 1994 | Yamada et al. | 356/400.
|
5361122 | Nov., 1994 | Kataoka et al. | 355/53.
|
5777722 | Jul., 1998 | Miyazaki et al. | 355/53.
|
5801835 | Sep., 1998 | Mitzutani et al. | 356/375.
|
5825043 | Oct., 1998 | Suwa | 355/55.
|
5969800 | Oct., 1999 | Makinouchi | 355/53.
|
6018384 | Jan., 2000 | Ota | 355/53.
|
Foreign Patent Documents |
4-116414 | Apr., 1992 | JP.
| |
Primary Examiner: Adams; Russell
Assistant Examiner: Brown; Khaled
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Claims
What is claimed is:
1. A plane position detecting method comprising the steps of:
moving a substrate in a direction intersecting an optical axis of a
projection optical system substantially at right angles;
feeding an area on the substrate into an image space of the projection
optical system;
detecting at least one of a position and an inclination of the substrate in
the optical axis direction;
determining when the area agrees with a focal plane of the projection
optical system; and
automatically selecting one of a first mode of performing the detection
during travel of the substrate and a second mode of performing the
detection in a state in which the area is substantially positioned within
the image space, the automatic selection being based on at least one of
shot layout information on the substrate and history information of
detecting results.
2. A method according to claim 1, further comprising setting a measurement
position on the substrate for detecting at least one of the position and
the inclination of the substrate in the optical axis direction within the
area.
3. A method according to claim 1, wherein the area is each of a plurality
of shots set on the substrate, and further comprising performing said
selecting step on the basis of shot layout information on the substrate.
4. A method according to claim 1, further comprising placing the substrate
on a stage traveling in a direction intersecting the optical axis of the
projection optical system, and performing said selecting step on the basis
of a position of the stage before starting travel of said substrate.
5. A method according to claim 1, further comprising, when either of the
first and second modes is switched over to the other in said selecting
step, notifying an operator of the mode switching.
6. A method according to claim 1, wherein the first mode includes a first
step traveling manner comprising steps of sequentially feeding a plurality
of shots set on the substrate as the area to the image space and detecting
a plane position of the area, and the second mode includes a second step
traveling manner of detecting the plane position of the area, and further
comprising selecting a subsequent step traveling manner for each shot, on
the basis of a history of a plane position correcting result obtained upon
execution of the step traveling.
7. A method according to claim 6, further comprising performing said
selecting step for each shot by the use of a threshold value derived from
the history of the connection results for the shots of a plurality of
substrates.
8. A method according to claim 6, further comprising placing the substrate
on the stage, which travels in the direction intersecting the optical axis
of the projection optical system substantially at right angles, and
adopting, as the plane position correction result, a result of measurement
of a vibrating state of an apparatus that includes the stage.
9. A method according to claim 6, further comprising, when either of the
first and second modes is switched over to the other in said selecting
step, notifying an operator of the mode switching.
10. A method according to claim 1, further comprising manufacturing a
semiconductor device by exposing the substrate to a pattern using the
projection optical system.
11. An exposure apparatus comprising:
a projection optical system;
a stage for moving a substrate in a direction intersecting an optical axis
of said projection optical system substantially at right angles, to feed
an area to be detected on the substrate to an image plane of said
projection optical system;
detecting means for detecting at least one of a position and an inclination
of the area to be detected relative to the direction of the optical axis,
and for producing a detection value result;
focusing means for detecting a plane position of the area to be detected on
the basis of the detection value, and for bringing the plane position into
focus with a focal plane of the projection optical system; and
selecting means for automatically selecting, as a step traveling manner for
feeding the area to be detected into the image space, one of (i) a first
step traveling manner of bringing the area to be detected into focus with
the focal plane on the basis of plane position information measured during
travel of the substrate, and (ii) a second step traveling manner of
bringing the area to be detected into focus with the focal plane on the
basis of the plane position information in a state in which the area to be
detected is substantially positioned, relative to the direction of travel,
with a prescribed position, the automatic selection being based on at
least one of shot layout information on the substrate and history
information of the detection results.
12. An apparatus according to claim 11, wherein said selecting means
selects one of the first and second step traveling manners as a step
traveling manner for sequentially feeding to the image space a plurality
of shots set on the substrate as the area to be detected.
13. An apparatus according to claim 12, wherein said selecting means
selects one of the first and second step traveling manners for each shot
on the basis of shot layout information on the substrate.
14. An apparatus according to claim 11, wherein said selecting means
selects one of the first and second step traveling manners on the basis of
a position of the stage immediately before a start of the substrate
travel.
15. An apparatus according to claim 11, further comprising range switching
means for switching over a detection range of said detecting means in
response to the selection by said selecting means, to change the detection
range and the detection time.
16. An apparatus according to claim 12, wherein said selecting means
selects a step traveling manner for each subsequent shot on the basis of a
history of plane position correction results upon performing the step
traveling.
17. An apparatus according to claim 16, wherein said selecting means adopts
a result of measurement of a vibrating state of said apparatus as a result
of the plane position correction upon executing the step traveling.
18. An apparatus according to claim 12, wherein said selecting means
selects, for each shot, a step traveling manner for subsequent shots by
the use of a threshold value derived from the history of correction
results for the shots of a plurality of substrates.
19. An apparatus according to claim 18, wherein said selecting means adopts
a result of measurement of a vibrating state of said apparatus as a result
of the plane position correction upon executing the step traveling.
20. An apparatus according to claim 16, wherein said selecting means
notifies an operator of mode switching when either of the first and second
modes is switched over to the other.
21. A method of detecting a plane position, comprising the steps of:
sequentially feeding a plurality of areas to be exposed on a substrate to
exposure positions;
detecting at least one of a position and an inclination of the substrate in
an exposure axis direction;
accomplishing plane positioning of the areas to be exposed at the exposure
positions, on the basis of the detection in said detecting step; and
switching over, for the substrate, a mode of the detection between one
during travel for feeding the substrate and one in a state in which the
areas to be exposed are substantially positioned at the exposure
positions.
22. A method according to claim 21, wherein said switching step is
performed on the basis of layout information of the areas to be exposed on
the substrate.
23. A method according to claim 21, wherein said switching step is
performed on the basis of a history of the results of plane position
detection conducted for another substrate.
24. A method according to any one of claims 21 to 23, further comprising
conducting exposure to the areas to be exposed, for which positioning has
been accomplished.
25. An apparatus for detecting a plane position, said apparatus comprising:
a feeder for sequentially feeding a plurality of areas to be exposed on a
substrate to exposure positions;
a detector for detecting at least one of a position and an inclination of
the substrate in an exposure axis direction;
plane positioning means for accomplishing plane positioning of the areas to
be exposed at the exposure positions, on the basis of the detection by
said detector; and
switching means for switching over, for the substrate, a mode of the
detection between one during travel for feeding the substrate and one in a
state in which the areas to be exposed are substantially positioned at the
exposure positions.
26. An apparatus according to claim 25, wherein said switching means
performs the switching on the basis of layout information of the areas to
be exposed on the substrate.
27. An apparatus according to claim 25, wherein said switching means
performs the switching on the basis of a history of the results of plane
position detection conducted for another substrate.
28. An apparatus according to any one of claims 25 to 27, further
comprising means for conducting exposure of the areas to be exposed, for
which positioning has been accomplished.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plane position detecting method of
detecting a position or an inclination (plane position) of a substrate
surface relative to an optical axis direction of a projection optical
system, and an exposing method and an exposure apparatus using the same.
2. Description of the Related Art
Improvements in productivity are now strongly demanded as the current
performance that is required in a semiconductor manufacturing apparatus,
particularly in a sequential travel type semiconductor exposing apparatus
known as a stepper. That is, a chip maker has to reduce the unit chip cost
so as to be able to prevent a memory cost meeting chip replacement, to
cope with the increase in the degree of integration along with the memory
trend.
Under these circumstances, an exposure apparatus maker must provide an
apparatus that can contribute to the improvement in productivity, in
addition to providing a high performance, with basic properties such as
resolution and positioning accuracy, and furthermore, must increase the
processing capacity per unit time, i.e., the number of processed wafers.
Methods of reducing the stepping time of a semiconductor exposure apparatus
used in a production site include methods proposed in Japanese Patent
Publication No. 4-50731 and Japanese Patent Laid-Open No. 4-116414. These
patent publications disclose methods of detecting a position or an
inclination of a substrate surface during step travel on an XY plane of a
substrate, such as a semiconductor wafer. With these methods, as compared
to a conventional method of detecting a position of a substrate relative
to a z-axis direction or an inclination of the XY plane through
confirmation of positioning of the substrate at an exposing position on
the XY plane, the timing of starting of the plane position correction
(i.e., the correction of a position in the z-axis direction or an
inclination in the XY plane) becomes earlier, thus making it possible to
reduce the stepping time as a whole.
There are also proposed a method of reducing the stepping time by
previously calculating a focus offset so that a measured value at a
measuring position during step travel of a substrate (hereinafter,
referred to as a "measuring position during travel") becomes equivalent to
a measured value at an exposing position of the substrate, and positively
utilizing a measured value of the plane position during travel, and a
method of reducing the stepping time through reduction of the measuring
time by performing measurement with a focus detection range limited by
taking into account a continuous step travel.
To date, an exposure wavelength for an exposure apparatus in the process
design for the manufacture of semiconductors has been selected
corresponding to the wiring rule: for example, an i-line stepper is used
for a 0.35-.mu.m rule, and a KrF excimer laser stepper for a 0.25-.mu.m
rule. That is, the manufacturing has been performed with the exposure
wavelength in use setting the limit of the resolution line width, and the
limit for the focal depth has inevitably been set to a value of about 1.0
.mu.m, which has been shared by the equipment and the process.
However, a new policy has recently been adopted, to continue to use a KrF
excimer laser in an exposure apparatus as the light source to serve as the
exposure technique with the next generation, having a 0.18-.mu.m rule.
There is also a move to utilize KrF excimer laser exposure until mass
production of 1-giga DRAMs of 0.1-.mu.m rule is achieved. The development
of refining techniques such as a phase shift mask and super-resolution, as
well as improvement of intra-chip flatness resulting from the adoption of
CMP (chemical-mechanical polishing) make important contributions to this
general trend. The use of CMP is reported to permit the reduction of a
chip stage in a trench structure to within about 50 nm, and it is now
possible to design a high numerical aperture (high-NA) lens having a
sharply reduced focal depth and to impart a resolution under that of the
wavelength of the exposure light being used.
To cope with the decrease in the focal depth resulting from the tendency
toward a high NA, on the other hand, it is necessary to further improve
the correction accuracy of the focusing and leveling. More specifically,
methods for assuring the accuracy of the chip stage on the process side
are diverse among the various semiconductor chip makers, including CMP,
PSM (phase shift mask) and RA (recessed array). The manufacture of chips
of the same generation with different margins of focal depth for the
individual semiconductor chip makers is about to begin. As a result, it
may be necessary to achieve a higher correction accuracy for a particular
process for individual semiconductor chip makers, particularly for a
process in which it is difficult to achieve perfect frames by the
application of the stacking method.
Under these circumstances, the present inventors have found that, in the
conventional method of performing corrective driving by offset-correcting
a measured value during travel, the offset reproducibility slightly varies
with the position of a shot on a wafer serving as the substrate, so that
the correction accuracy may, in some cases, deviate from the standard,
depending upon the position of the shot on the wafer.
This is chiefly attributable to the fact that, because the exterior shape
of the wafer itself has been scaled up in order to cope with a 300-mm
wafer and the like, and the amplitude (Z-direction) of the structural
deformation in the tilting direction of the stage becomes larger along
with the expansion of the wafer in the radial direction, a difference
occurs in reproducibility of any offset between the wafer periphery and
inside portions of the wafer. This instability, which is within a
tolerable range in the conventional accuracy, leads to a non-negligible
amount when covering a residual chip stage, as mentioned above, on the
exposure apparatus side.
In a conventional method of focusing by limiting the focus detection range
to reduce the stepping travel time, in a sequence other than exposure,
such as during the execution of a step command after execution of a user
operation, the surface to be detected may sometimes exceed the focus
detection range, which may cause stoppage of the sequence.
SUMMARY OF THE INVENTION
In view of the foregoing problems associated with the conventional art, the
present invention has an object to provide a plane position detecting
method that permits detection of a position or an inclination of a
substrate surface at a high accuracy and a high speed in a process
subjected to strict requirements for focal depth beyond current pattern
refinement trends or the like, and an exposing method and an exposure
apparatus using the same.
To achieve the aforementioned object, the plane position detecting method
of the present invention comprises the steps of moving a substrate in a
direction intersecting an optical axis of a projection optical system
substantially at right angles, feeding an area on the substrate into an
image space of the projection optical system, detecting at least one of a
position and an inclination of the substrate in the optical axis
direction, determining when the area agrees with a focal plate of the
projection optical system, and selecting one of a first mode of performing
the detection during travel of the substrate and a second mode of
performing the detection in a state in which the area is substantially
positioned within the image space. This plane position detecting method is
particularly applicable to a sequential traveling type semiconductor
exposure apparatus (stepper).
In another aspect of the invention for achieving the aforementioned object,
there is provided a plane position detecting method comprising the steps
of sequentially feeding a plurality of areas to be exposed on a substrate
to exposure positions, detecting at least one of a position and an
inclination of the substrate in substantially the exposure optical axis
direction, accomplishing plane positioning of the areas to be exposed at
the exposure positions, on the basis of the detection, and switching over,
within the substrate, a mode of the detection between one during feeding
travel for feeding the substrate and one in a state in which the areas to
be exposed are substantially positioned at the exposure positions.
An exposure apparatus of a preferred embodiment of the invention comprises
a projection optical system, a stage which travels in a direction
intersecting the optical axis of the projection optical system
substantially at right angles, while mounting a substrate, thereby feeding
an area to be detected on the substrate to an image plane of the
projection optical system, a detector which detects at least one of a
position and an inclination relative to the optical axis direction of the
substrate and produces a detection value, and a focusing unit which brings
the area to be detected into focus with a focal plane of the projection
optical system, on the basis of the detection value of the detector. The
exposure apparatus has two manners of stepping travel that can be selected
by selecting means: one (type B) of bringing the area to be detected into
focus with the focal plane on the basis of the plane position information
measured during travel, and another (type A) of bringing the area to be
detected into focus with the focal plane on the basis of the plane
position information in a state in which the area to be detected has
substantially been positioned, relative to the traveling direction, at the
image plane position of the projection optical system.
By properly selecting one of the speed-oriented manner of stepping travel
(type B) of bringing the area to be detected into focus with the focal
plane on the basis of the plane position information measured during
travel, and the accuracy-oriented manner of stepping travel (type A) of
bringing the same into focus with the focal plane on the basis of the
plane position information in a state in which the area to be detected has
substantially been positioned at the image plane position optical system,
the above-mentioned problems can be solved.
High-speed and high-accuracy automatic chip exposure job design is possible
by previously setting a manner of stepping travel for each shot on the
basis of layout information, in terms of the selection of a manner of
stepping travel, and bringing each shot in focus with the focal plane in
accordance with the thus previously set manner of stepping travel.
It is possible to avoid stoppage of the exposure sequence, by selecting a
manner of stepping travel in response to the position of the stage
immediately before a start of stepping travel, so as to bring the area to
be detected into focus with the focal plane.
It is also possible to change the detection range and the detection time,
respectively, by switching over the detecting range of the focus detecting
means in response to the manner of stepping travel, and to prepare a chip
processing job compatible with both accuracy and productivity by taking
into account the processing time as a whole.
An the exposure apparatus of another preferred embodiment of the invention
comprises a projection optical system, a stage holding a substrate, the
stage traveling in a direction intersecting the optical axis of the
projection optical system substantially at right angles, thereby feeding a
shot area on the substrate to an image plane of the projection optical
system, a detector which detects at least one of a position and an
inclination relative to the optical axis direction of the substrate, and a
focusing unit which brings the shot area into focus with the focal plane
of the projection optical system. This exposure apparatus has (i) a
speed-oriented manner of stepping travel (type D) of bringing the shot
area into focus with the focal plane on the basis of plane position
information measured during travel, and includes automatically determining
a correction accuracy, and (ii) an accuracy-oriented manner of stepping
travel (type C) of bringing the shot area into focus with the focal plane
on the basis of plane position information in a state in which the shot
area has substantially been positioned, relative to the traveling
direction, at the image plane position of the projection optical system.
The aforementioned problems can be solved by automatically selecting the
optimum manner of stepping travel from the measuring history of each shot
area.
When using the type C manner of stepping travel, for example, if a
satisfactory correction accuracy is determined to be available by the type
D manner of stepping travel judged from the history of the plane position
information during travel, then, the manner is switched over to the type D
manner of stepping travel. When using the type D manner of stepping
travel, if a satisfactory correction accuracy is determined not to be
available by the type D manner of stepping travel judged from the history
of the plane position information after focusing of the shot area, then,
the manner is changed over to the type C manner of stepping travel. It is,
therefore, possible to provide an exposure apparatus permitting
high-accuracy and high-speed plane position correction, for example, by
setting the type C manner of stepping travel for each shot area on the top
wafer of a lot, and constantly switching over the manner of stepping
travel on the basis of the history of the plane position information.
According to such an embodiment, it is possible to accurately determine an
inclination of an area to be detected relative to the image plane or a
shift in the height direction by the use of measured values during travel.
Since a manner of stepping travel is previously selected in view of the
reproducibility of offset, it is possible to achieve a job design, taking
into account both the correction accuracy and processing efficiency for
the substrate as a whole. Accurate and prompt processing can be carried
out, to transfer a fine pattern in a future high-NA exposure apparatus, by
creating a confirmation timing without extending the stepping travel time,
regarding the final corrected state of focus.
In another aspect, to achieve the foregoing objects, the present invention
provides a method of detecting a plane position, comprising the steps of
sequentially feeding a plurality of areas to be exposed on a substrate to
exposure positions, detecting at least one of a position and an
inclination of the substrate in an exposure axis direction, accomplishing
plane positioning of the areas to be exposed at the exposure positions, on
the basis of the detection in the detecting step, switching over, within
the substrate, a mode of the detection between one during travel for
feeding the substrate and one in a state in which the areas to be exposed
are substantially positioned at the exposure positions. The switching step
can be performed on the basis of layout information of the areas to be
exposed on the substrate. The switching step also can be performed on the
basis of a history of the results of plane position detection conducted
for another substrate.
In another aspect, the method can further comprise conducting exposure to
the areas to be exposed, for which positioning has been accomplished.
In yet another aspect, the present invention provides an apparatus for
detecting a plane position. The apparatus includes a feeder for
sequentially feeding a plurality of areas to be exposed on a substrate to
exposure positions, a detector for detecting at least one of a position
and an inclination of the substrate in an exposure axis direction, plane
positioning means for accomplishing plane positioning of the areas to be
exposed at the exposure positions, on the basis of the detection by the
detector, and switching means for switching over, within the substrate, a
mode of the detection between one during travel for feeding the substrate
and one in a state in which the areas to be exposed are substantially
positioned at the exposure positions. In one aspect, the switching means
can perform the switching on the basis of layout information of the areas
to be exposed on the substrate. In another aspect, the switching means can
perform the switching on the basis of a history of the results of plane
position detection conducted for another substrate. The apparatus can
further include means for conducting exposure of the areas to be exposed,
for which positioning has been accomplished.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic, partial view of a step-and-repeat type reduction
projection exposure apparatus of an embodiment of the present invention;
FIG. 2 illustrates an arrangement of exposure position measuring points set
in an area to be exposed in the embodiment shown in FIG. 1;
FIG. 3 illustrates an arrangement of measuring points during travel set in
an area to be exposed in the embodiment shown in FIG. 1;
FIG. 4 illustrates exposure positions arranged on a wafer, correspondence
of the individual measuring positions, and stepping travel between shots;
FIG. 5 is a flowchart illustrating a speed-oriented stepping travel of the
embodiment shown in FIG. 1;
FIG. 6 is a flowchart illustrating an accuracy-oriented stepping travel of
the embodiment shown in FIG. 1;
FIG. 7 is a flowchart illustrating an embodiment of the invention in which
stepping travel is switched over for each shot on the basis of layout
information;
FIG. 8 is a flowchart illustrating an embodiment of the invention of a
stepping travel selecting operation;
FIG. 9 is a flowchart illustrating an embodiment of the invention in which
the manner of stepping travel is automatically switched over for each shot
on the basis of past stepping history information;
FIG. 10 is a flowchart illustrating an embodiment of the invention of a
stepping travel selecting operation (type C);
FIG. 11 is a flowchart illustrating an embodiment of the invention of a
stepping travel selecting operation (type D);
FIG. 12 illustrates the flow of manufacturing a semiconductor device; and
FIG. 13 is a flowchart illustrating the flow, in detail, of the wafer
process shown in FIG. 12.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a schematic, partial view of a step-and-repeat type reduction
projection exposure apparatus of the present invention. In FIG. 1,
reference numeral 1 represents a reduction projection lens, and an
exposure axis thereof is shown by dotted line AX in the drawing. The
reduction projection lens 1 projects a circuit pattern of a reticle (not
shown) to, for example, a size reduced to one fifth, and forms a circuit
pattern image on a focal plane thereof. The optical axis AX is parallel to
the Z-axis direction in FIG. 1. Reference numeral 2 represents a
semiconductor wafer having a resist coated on the surface thereof. A
plurality of areas to be exposed (shots) having the same patterns formed
in a preceding exposure process are arranged on the upper surfaces of
semiconductor wafer 2.
In FIG. 1, reference numeral 3 represents a wafer stage for mounting wafer
2. The wafer 2 is attracted by (e.g., by vacuum), and fixed to, the wafer
stage 3. The wafer stage 3 comprises an X-stage moving in the X-axis
direction, a Y-stage moving in the Y-axis direction, and a
.theta.-Z-leveling stage moving in the Z-axis direction and rotating
around axes parallel to the X, Y and Z-axis directions. The X, Y and
Z-axes intersect each other at right angles.
By driving the wafer stage 3, therefore, the surface position of the wafer
2 can be adjusted in the optical axis AX direction (Z-axis direction) of
the reduction projection lens 1, and in the X, Y or .theta. direction
within a plane crossing the optical axis AX at right angles (i.e., the X-Y
plane), and further, it is also possible to adjust also the inclination
relative to the focal plane of the reduction projection lens 1, i.e.,
relative to the circuit pattern image (i.e., the rotating directions
around the X- and Y-axes).
In FIG. 1, reference numerals 4 to 11 represent elements of detectors that
are provided to detect the surface position and inclination of the wafer
2: 4 representing an illuminating light source, which is a high-luminance
light source, such as a light-emitting diode or a semiconductor laser; and
5 an illuminating lens. A light beam emitted from the light source 4 forms
parallel luminous fluxes through the illuminating lens 5 and illuminates a
mask 6 having a plurality (five, for example) of pinholes formed therein.
The luminous fluxes having passed through the pinholes of the mask 6 enter
a folding mirror 8 via an image forming lens 7, and after having their
direction changed through the folding mirror 8, illuminate the surface of
the wafer 2. At this point, the image forming lens 7 and the folding
mirror 8 form images of the plurality of pinholes of the mask 6 on the
wafer.
As shown in FIG. 2, the luminous fluxes having passed through the plurality
of pinholes irradiate five points (71 to 75), including the center of an
area 100 of the wafer 2 to be exposed, and are reflected from these
points. That is, in this embodiment, five pinholes are formed in the mask
6, and positions of the five measuring points (71 to 75), including the
center in the area to be exposed 100, are measured, as will be described
later.
Referring back to FIG. 1, the luminous fluxes reflected from the measuring
points (71 to 75) change their direction at a folding mirror 9, and then
enter a position detecting element 11, formed by two-dimensionally
arranging photodetecting elements, via a detecting lens 10. The detecting
lens 10 forms images of the pinholes of the mask 6 on the position
detecting element 11 in cooperation with the image forming lens 7, the
folding mirror 8, the wafer 2 and the folding mirror 9. The mask 6, the
wafer 2 and the position detecting element 11 are arranged in optically
conjugate positions with respect to each other.
When the arrangement shown schematically in FIG. 1 is difficult from the
point of view of optical layout, a plurality of position detecting
elements 11, corresponding to the individual pinholes, may be arranged.
The position detecting elements 11 comprise two-dimensional CCDs or the
like, and can independently detect incident positions of the plurality of
luminous fluxes via the plurality of pinholes onto light receiving
surfaces of the position detecting elements 11. A change in position of
the wafer 2 in the direction of the optical axis AX of the reduction
projection lens 1 can be detected as a shift of the incident position of
the plurality of luminous fluxes onto the position detecting elements 11.
As a result, the positions of the wafer 2 at the fine measuring points (71
to 75) in the area to be exposed 100 in the direction of the optical axis
on the wafer surface are entered into a controller 13, via a plane
position detecting apparatus 14, as output signals from the position
detecting elements 11.
Displacement of the wafer stage 3 in the X-axis and Y-axis directions is
measured by a known method by the use of a reference mirror 15 provided on
the wafer stage and a laser interferometer 17, and a signal representing
an amount of displacement of the wafer stage 3 is entered into the
controller 13 from the laser interferometer 17 via a signal line. The
travel of the wafer stage 3 is controlled by a stage drive 12. The stage
drive 12 receives an instruction signal from the controller 13 via a
signal line, and servo-drives the wafer stage 3 in response to this
signal. The stage drive 12 has a first driving unit and a second driving
unit: it adjusts the position (X, Y) and the rotation (.theta.) within a
plane intersecting the optical axis AX of the wafer 2 at right angles by
the use of the first driving unit, and adjusts the position (Z) and the
inclination (.alpha., .beta.) in the direction of the optical axis AX of
the wafer 2 by the use of the second driving unit.
The plane position detecting apparatus 14 processes output signals from the
position detecting element 11 (plane positional data), and detects the
surface position of the wafer 2. The result of this detection is
transferred to the controller 13: the second driving unit of the stage
drive 12 is operated by a prescribed instruction signal, thereby adjusting
the position and the inclination of the wafer 2 in the optical axis AX
direction.
The focus detecting position in this embodiment will now be described. In
this embodiment, two measuring points are set: a measuring point during
travel (position) used basically for calculating a corrected amount of
driving, and an exposure position measuring point that serves as a
reference for calculating offset, mainly for the purpose of correcting a
value measured at the aforementioned position, so as to be equivalent to
the measured value at the exposure position.
First, the exposure position measuring point is illustrated in FIG. 2. A
measuring point 71 is substantially at the center of the area 100 to be
exposed, and intersects the optical axis AX at the exposure position. The
remaining measuring points 72 to 75 are located along the periphery of the
area 100 to be exposed.
In all of the shots in a wafer, the exposure position measuring points to
be covered (i.e., measured by sensors using detecting portions of the
position detecting element 11) are stepped in shape. Therefore, an offset
value, dependent upon the step shape for each sensor when the image
forming plane of the reduction projection lens 1 is used as a reference
plane, is primarily determined for each sensor. Accordingly, when an
inclination and a position in the height direction of a chip are detected
for a stage positioned at the exposure position, it is not necessary to
change the offset for each shot.
An example of an in-travel measuring point for measuring during traveling
is illustrated in FIG. 3. In FIG. 3, a measuring point 81 is measured
during travel, in place of the measuring point 71, at a position
intersecting with the optical axis AX. More specifically, the direction of
travel of wafer 2 in the drawing is from right to left, and, for the
individual measuring points 71 to 75, positions of in-travel measurement
shift to the right on the chip 100, as represented by measuring points 81
to 85.
When conducting measurement during stepping travel, as mentioned above, the
detectors (4 to 11) would measure the surface having a step different from
that when the chip 100 is at the exposure position, strictly speaking, by
an amount corresponding to a change in the relative position of the chip
100. Even a shot layout containing only twelve shots on the wafer 2, as
shown in FIG. 4, has five different measuring points (left, right, top
right, top left and top), and may even have up to eight in-travel
measuring points.
In addition, a change in the main body structure between in-travel
measuring points is equal to a Z-direction displacement available by
multiplication by the shot position from the center, as derived from the
relationship between the shot position (X, Y) on the wafer 2 and the
posture deformation (.alpha., .beta.) at that point, even when the posture
deformation (.alpha., .beta.) is the same for all runs of stepping travel,
resulting in different values for different shots. This main body
deformation, however, being confirmed to exhibit a high reproducibility,
can be controlled as an offset for each shot, just as an offset resulting
from a step in a shot.
The two manners of stepping used in this embodiment including the
speed-oriented manner of stepping (type B) and the correction
accuracy-oriented manner of stepping (type A) will now be described with
reference to the flowcharts shown in FIGS. 5 and 6.
In the speed-oriented manner of stepping (type B) shown in FIG. 5, the
stage 3 starts stepping travel of the wafer 2 at step S401. At step S402,
it is determined whether or not the wafer 2 has reached the in-travel
measuring position before the wafer 2 reaches the target position, while
always reading in the current position of the stage 3 via the laser
interferometer 17. When the wafer 2 is determined to have reached the
focus measuring position during travel, the detectors (4 to 11) perform
focus measuring at step S403. Then, at step S404 the measured value is
corrected by the use of an offset unique to a determined in-travel
measurement periphery, i.e., an offset caused by an apparatus deformation
in the state of the apparatus at a target position, such as the exposure
position, or by a step in the substrate at a position other than the
target position (hereinafter referred to as the "focus offset 1"). After
calculating a corrected amount of driving from data after correction, a
determination is repeated, at step S405, on the basis of measured values
of the detectors (4 to 11) until the wafer 2 reaches the proximity to a
specified target position in terms of the position in the Z-axis direction
and the inclination. When the wafer 2 is confirmed to have reached the
proximity location, completion of the final positioning is confirmed at
step S406.
The correction accuracy-oriented manner of stepping (type A) will now be
described with reference to FIG. 6. At step S501, the stage 3 starts
stepping travel of the wafer 2, and at step S502, a determination is made
as to whether or not the wafer 2 has reached the in-travel measuring
position, before the wafer 2 reaches the target position, while always
reading in the current of the stage 3 via the laser interferometer 17.
When the in-travel focus measuring position is determined to have been
reached, at step S503, a determination is repeated until the proximity to
a specified target position is reached. Only after confirming that the
proximity to the specified target position has been reached, do the
detectors (4 to 11) perform focus measurement at step S504. Then, the
measured value is corrected by the use of a previously determined offset,
i.e., an offset caused by a step in the substrate at a target position,
such as the exposure position, and an amount of corrective driving is
calculated from data after correction. At step S505, the aforementioned
second drive conducts a corrective driving, and then at step S506, the
completion of final positioning is confirmed.
These two manners of stepping differ in that, while the former conducts
measurement during travel and starts early correction of the plane
position of the stage 3 (wafer 2), the latter starts correction of the
plane position of the stage 3 (wafer 2) upon reaching the proximity to the
target position. In FIG. 6, step S502 is provided to show the absence of
processing upon reaching the measuring point during travel. The sequence
may, however, comprise waiting to reach the proximity to the target
position at step S503, immediately following step S501.
Exposing operations of the apparatus shown in FIG. 1 will now be described
with reference to the flowchart illustrated in FIG. 7. First, at step
S701, the job is started, and at step S702, it is determined and selected,
for each shot, which of the two manners of stepping travel is to be used:
i.e., the accuracy-oriented manner of stepping travel (type A: correcting
the focus at the exposure position or a position where the observation
position is reached) and the speed-oriented manner of stepping travel
(type B: correcting the focus at the in-travel measuring position). More
specifically, when the stepping travel direction of the wafer 3 is in the
X-axis direction, the accuracy-oriented type A is set for the shots at the
line ends, and the speed-oriented type B, for the other shots.
For example, when the shot arrangement image is as shown in FIG. 4, the
type B is set for SH4, SH5, SH8 and SH9, and type A, for the eight
remaining shots. While the ratio of the accuracy-oriented type A is rather
high when the number of shots is small, as in this example, when
considering exposure of a large-diameter, for example, a 300 mm wafer 256
M chip that requires careful selection of a manner of stepping travel as
described in this embodiment, the speed-oriented type B stepping travel
can be selected for 76 shots (about 80%) out of 96 shots in total.
In an actual layout for mass production, this ratio becomes increasingly
high because of shrinkage and cut-down. However, it may become necessary
to adopt the accuracy-oriented type A for the accuracy of the next inside
ship. For the determination in this case, the manner of stepping travel
may be determined by assessing the stepping travel direction axial
coordinates of the step position coordinates, i.e., in the case of
stepping travel in the X-axis direction, the X-coordinates of that shot
with a threshold value.
A manner of stepping travel is selected for each shot as described above,
and then, at step S703 in FIG. 7, a wafer 2 in a lot is transferred onto
the stage 3, and the sequence thereof is checked. If the set wafer 2 is
the first one of that lot, then at step S704, a focus offset necessary for
focus measurement in the two aforementioned manners of stepping travel is
measured by a conventional method. With these operations, the selection of
a manner of stepping travel and the measurement of focus offset for each
shot of the wafer 2 processed within the lot are completed.
The exposure processing for each wafer in the lot will now be described. At
step S705, preparations are made for transferring to the next exposure
shot, and a position of that shot, a manner of stepping travel and a focus
offset are set. At step S705, the adopted manner of stepping travel is
checked: the stepping manner is switched over to the type A for an
accuracy-oriented step, and to the type B for a speed-oriented step.
At step S708, the positioning position before exposure is finally
confirmed, and exposure is executed at step S709. At step S710, the
completion of exposure for all the shots is checked, and if not completed,
the flow of steps S705 to S706 is repeated over again. When all of the
shots have been exposed, the wafer is taken out at step S711. If the lot
is not as yet completed, the process returns to step S703 to load the next
wafer and continue the aforementioned exposure flow.
Cases in which focus detection is carried out on the exposure apparatus
include, in addition to the above-mentioned case in which projection
exposure is performed while continuously applying a reticle pattern onto
the wafer 2 during step-and-repeat exposure, a case in which, after an
interruption of exposure by intervention of an external operation, such as
execution of a test command by the user (e.g., by the semiconductor chip
maker), the exposure sequence is resumed, and a case in which, after
measuring a mark showing a position on the wafer 2 or on the stage 3, such
as measurement of global alignment, the exposure sequence is resumed. In
these cases, when the stepping travel distance of the wafer 2 (stage 3) is
long, the Z-direction position of the wafer 2 is not assured because of
deformation (e.g., surface irregularities) of the wafer 2 or the presence
of an external operation. It is, therefore, necessary that the detection
range of focus by the detectors (4 to 11) be wider than the detection
range upon continuous or step-and-repeat exposure.
In the case of a measurement different from continuous or step-and-repeat
exposure, the measuring position can later be on the periphery of the
wafer. The requirements regarding accuracy and speed differ between the
stepping travel for continuous or step-and-repeat exposure and the other
stepping travel, as described above. In the latter case, it is necessary
to select the type A stepping travel, in which focus measurement and
correction are accurately carried out at a stationary position with a
widened detection range.
Another embodiment of the invention will now be described with reference to
FIG. 8. FIG. 8 illustrates a functional module of a software program for
executing stepping travel conditions. Prerequisites for starting this
module are as follows.
First, when a user operation is present, the condition of continuous
stepping travel (stepping travel upon step-and-repeat exposure) is
impaired, and therefore, the type A stepping travel would be selected for
the next shot. In this case, input of the user operation is detected, and
an internal stepping travel manner selecting flag is turned on (selecting
the type A). For global alignment measurement, it is possible to turn on
the stepping travel manner selecting flag in terms of software, since a
sequence has internally been determined. The stepping travel manner
selecting flag is set for each step in the sequence, as described above,
as a result of a determination of an external operation or an internal
sequence.
Under these conditions, the functional module for stepping travel shown in
FIG. 8 is called, and started at step S801. Then, at step S802,
information necessary for stepping travel of the wafer 2, such as a target
position, is set. Then, the stepping travel manner selecting flag, which
is set when a special step is necessary, is checked at step S803. If it is
on (selecting the type A), the focus detecting range of the detectors (4
to 11) is expanded at step S804, and at step S805, the accuracy-oriented
type A stepping travel manner is executed. If the flag is off, indicating
continuous stepping travel, the speed-oriented type B stepping travel
manner is started at step S805. Irrespective of the selected manner of
stepping travel, after confirmation of the completion of positioning at
step S805, stepping travel of the wafer 2 is completed by turning off the
stepping travel manner selecting flag at step S806.
In the above description, the measuring range of the detectors (4 to 11)
has been expanded when the stepping travel manner selecting flag has been
turned on. However, in the case of a detector of which the measuring time
is not dependent upon the range, such as an analog sensor including a PSD
(position selecting diode), the selection of the type A, which is less
susceptible to the influence of vibration or the type B, which requires an
offset to be previously measured may be made with a common detection range
as it is.
A manner of accuracy-oriented stepping travel for automatic determination
(type C), which is one of the stepping travel manners in the next
embodiment (shown in FIG. 9), will be described in detail in accordance
with the flowchart shown in FIG. 10, with reference to FIGS. 1 to 4.
First, a target position of the stage 3 is set in the controller 13 so that
an exposure shot 100 comes to the exposure position below the lens 1, and
then, travel of the wafer stage 3 is started (S1001). Then, the position
of the exposure shot on the XY plane is monitored by the laser
interferometer 17 and the controller 13. When the exposure shot reaches a
prescribed position suitable for detecting the in-travel plane position,
the detectors (4 to 11) conduct a first run of plane position detection
(i.e., in-travel plane position detection) (S1002).
The in-travel plane position detection detects the plane position with
respect to an image plane of the lens 1 of the exposure shot (exposure
area) at the target stage position. In this manner of stepping travel
(type C), the detection results of the detectors (4 to 11) are used mainly
for calculating the plane position detecting accuracy during travel of the
stage, and not for adjusting the height or inclination of the wafer 2.
The operations during stepping travel have now been completed. After
confirming the completion of positioning of the wafer stage 3 on the XY
coordinates (S1003), the detectors (4 to 11) perform a second run of the
plane position detection (i.e., stationary plane position detection)
(S1004). After the stationary plane position detection, the height and
inclination of the wafer 2 are adjusted by using the detection results
(S1005). A deviation from the exposure image plane of the lens 1 (i.e.,
the in-travel plane position detection error) is calculated for a case in
which the height and the inclination of the wafer 2 are adjusted by the
use of the results of the in-travel plane position detection from
differentiation of data obtained by correcting the results of the
in-travel plane position detection by the use of the focus offset 1 and
data obtained by correcting the results of the stationary plane position
detection by the use of the focus offset 2. The results of these
calculations are classified for each exposure area 100 and stored in the
controller 13 (S1006).
The speed-oriented manner of stepping for automatic determination (type D),
one of the manners of stepping travel in this embodiment, will now be
described in detail in accordance with the flowchart shown in FIG. 11.
First, travel of the wafer stage 3 is started after setting a target stage
position in the controller 13, as in the aforementioned manner of stepping
travel (type C). As in the type C, the detectors (4 to 11) perform a first
run of plane position detection (i.e., in-travel plane position detection)
at a prescribed position (S1102). Then, the height and the inclination of
the wafer 2 are adjusted by a second driving unit by the use of data
obtained by correcting the detection results with the aforementioned
correction offset (S1103).
After the completion of this adjustment, and after confirming the
completion of positioning of the wafer stage 3 on the XY coordinates, the
detectors (4 to 11) carry out a second run of plane position detection
(i.e., stationary plane position detection) (S1105). Detection of the
stationary plane position has a main object to measure an error in
adjustment of the height and the inclination by the use of the results of
the in-travel plane position detection, and is not employed for adjusting
the height or the inclination of the wafer 2. Finally, an error in the
in-travel plane position detection is calculated from the results of the
stationary plane position detection, and the results are classified for
each exposure area 100 and stored in the controller 13 (S1106).
An embodiment using the above-mentioned manners of stepping travel will now
be described in detail in accordance with the flowchart shown in FIG. 9.
First, at step S901, a patterned wafer 2 is fed onto a wafer stage 3 by a
wafer feeder (not shown). At step S902, positional shifts in the X and Y
directions relative to the optical axis AX and the reference layout of the
wafer stage 3 are measured by an alignment mechanism (not shown). Lattices
for stepping are calculated to match with the lattice of a shot
arrangement already transferred onto the wafer 2, and stored in the
controller 13. As a result, an offset dependent upon a step shape for each
focus sensor (each detecting portion of the position detecting element 11)
in each shot at the exposure position can primarily be determined.
Then, it is determined whether or not the wafer 2 set on the apparatus
shown in FIG. 1 is the first one (step S903). If it is the first wafer, a
measurement offset for calculating the plane position of the image plane
reference at the exposure position is calculated from the focus detection
value obtained when the shot 100 is at the exposure position. Further,
another measurement offset for calculating the plane position of the image
plane reference of the exposure position is calculated from the focus
detection value during travel (step S904). As a result, it is possible to
accurately detect the plane position of the image plane reference at the
exposure position for the exposure position or for a prescribed position
during travel.
Then, at step S905, the controller 13 calculates an in-travel plane
position detecting accuracy from the history of in-travel plane position
detection errors stored therein, and automatically selects a manner of
stepping travel of the C or D type by determining the same with a
threshold value or the like. This selection is made automatically for all
of the shots from the history of the in-travel plane position detecting
errors so far stored, every time a second or subsequent wafer is fed.
History data, therefore, increases accordingly, as more wafers are
processed, and reliability is automatically improved. As a result, as
compared with a conventional empirical selection, it is possible to make a
selection at a higher accuracy and a higher immediacy.
On the basis of the results of the automatic selection of the manner of
stepping travel, a target stage position is set in the controller 13 so
that the next exposure shot 100 comes to the exposure position below the
lens 1. Then, travel of the wafer stage 3 is started (step S906). In
response to the results of the automatic selection of the manner of
stepping travel of the exposure shot 100, the type C manner of stepping
travel (step S909) or the type D manner of stepping travel (step S908) is
executed. After confirming the completion of positioning of all six axes
after stepping travel, exposure is carried out at step S910.
At step S911, a loop control is performed to determine whether or not
exposure of all of the shots has been completed. If exposure of all of the
shots of the wafer 2 has not yet been completed, the wafer stage 3 is
moved to the next exposure shot (step S906). If completed, the wafer on
the wafer stage 3 is taken out (step S912). Similarly, at step S913, a
loop control is performed to determine whether or not exposure of all of
the wafers has been completed. If not completed, the next wafer is fed
(step S901), and if completed, the processing comes to an end.
In this embodiment, the shot position where the manner of travel is
switched over to the accuracy-oriented mode is determined from the point
of view of the apparatus. When the production efficiency of the chips as a
whole varies, the ratio of the speed-oriented stepping travel may be
reduced under the effect of the automatic selection of stepping travel. In
such a case, it is possible to return to the original chip productivity by
cleaning a chuck or the stage, for example.
To cope with such circumstances, the following method is used in this
embodiment. In FIG. 1, a database containing processing information is
generated for each wafer regarding processing of a lot in a host terminal
(not shown) connected to the controller 13 to retain therein Yes/No
information for shots subjected to switching of the manner of stepping
travel. After processing of the lot, the operator can check the processing
time or the correction accuracy, and can determine a necessity of
maintenance of the apparatus by accessing this database.
Another notifying method consists of calculating the switching frequency of
the stepping manner during processing of the lot and the ratio of the
speed-oriented stepping travel within a wafer, making a determination on
the basis of a threshold value, and when a need to notify is determined,
immediately notifying the operator on the host terminal screen or by the
use of another display. The operator can, from time to time, change this
threshold value in response to the degree of necessity required by the
lot.
Yet another embodiment of the invention will now be described. The exposure
apparatus of this embodiment includes means for measuring vibration of the
stage, which forms a main cause of fluctuations of the accuracy upon
in-travel detection of the plane position. If an electrostatic capacitive
sensor is used, for example, as the vibration measuring instrument, it is
possible to conduct real-time measurement of inclination. Stage vibration
during detection of the plane position in stepping travel of each exposure
shot is, therefore, measured by a vibration measuring instrument.
Upon stepping travel for each exposure shot of the next wafer, a manner of
stepping travel is selected on the basis of values of vibration measured
as described above. According to this embodiment, stage vibration itself,
which is a main cause of vibration of the accuracy in plane position
detection in travel, is used as a reference for the selection of a manner
of stepping travel. It is, therefore, possible to estimate an accuracy
upon in-travel plane position detection, even from a measured vibration
value of a single wafer and thus, to determine a manner of stepping travel
at an early timing.
An embodiment of a method for producing a device, such as a semiconductor
device, by the use of the above-mentioned exposure apparatus or exposure
method will now be described. FIG. 12 illustrates a manufacturing
flowchart for micro-devices (e.g., semiconductor chips, such as ICs and
LSIs, a liquid crystal panel, a CCD, a thin-film magnetic head and a
micromachine). At step 1 (circuit design), a pattern design is performed
for a device. At step 2 (preparation of mask), a mask having the designed
pattern formed thereon is prepared. At step 3 (manufacture of wafer), on
the other hand, a wafer is manufactured from a material such as silicon or
glass.
Step 4 (wafer process) is called a pre-process, in which an actual circuit
is formed on the wafer by lithographic technology, by the use of the thus
prepared mask and wafer. At step 5 (assembly), which follows, a
semiconductor chip is manufactured from the wafer prepared at step 4, and
includes an assembly substep (dicing or bonding) and a packaging substep
(sealing of chip). At step 6 (inspection), an operation confirming test, a
durability test and the like are carried out on the semiconductor device
prepared at step 5. The semiconductor device is completed through these
step, and shipped (step 7).
FIG. 13 illustrates a detailed flowchart of the aforementioned wafer
process discussed above with respect to step 4 of FIG. 12. At step 11
(oxidation), the wafer surface is oxidized. At step 12 (CVD), an
insulating film is formed on the wafer surface by chemical vapor
deposition. At step 13 (forming electrodes), electrodes are formed on the
wafer by vapor deposition. At step 14 (ion implantation), ions are
injected into the wafer.
At step 15 (resist processing), a photosensitizer is coated onto the wafer.
At step 16 (exposure), a circuit pattern of a mask is printed onto the
wafer and exposed by an exposure apparatus adopting the plane position
detecting method as described above. At step 17 (development), the exposed
wafer is developed. At step 18 (etching), the developed portions other
than the resist image are ground off or otherwise removed. At step 19
(resist peeling), any portion of the resist that has become unnecessary
after etching is removed. Multiple circuit patterns are formed on the
wafer by repeating these steps. With the production method of this
embodiment, it is possible to manufacture, at a low cost, devices of a
high degree of integration that have so far been difficult to manufacture.
Except as otherwise disclosed herein, the various components shown in
outline or in block form in the Figures are individually well known and
their internal construction and operation are not critical either to the
making or using of this invention or to a description of the best mode of
the invention.
While the present invention has been described with respect to what is at
present considered to be the preferred embodiments, it is to be understood
that the invention is not limited to the disclosed embodiments. To the
contrary, the invention is intended to cover various modifications and
equivalent arrangements included within the spirit and scope of the
appended claims. The scope of the following claims is to be accorded the
broadest interpretation so as to encompass all such modifications and
equivalent structures and functions.
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